Not to rain on your parade but many ceiling fan companies make an additional module that is designed specifically to work with the mounding layer between the fan and lights, the one I have allows your classic chain operation but also came with a remote, it also allows 3 level dimming via the chain switch and 3 fan speeds bia the other fan switch or variable dimming/slowing via the remote.
I would suspect since these units are available in all but the most low end models the market would be thin for such a device, there are also remote only third party products that mount in a code approved gang box to the electical box the fan is wired to in the ceiling.
However in the third party option there are two drawbacks, you have to have access to the ceiling and if you have that you could just as soon you 2 X-10 inlines, but the other drawback is that you have to pull the fan down and find the hat wire leading to the lights and fan motor, cut them and then wire with separtly to the fan.
Given that a ceiling fans that come with the split operation option already in them can be found for under 100 bucks and only require that you replace the fan with no need for ceiling access, it would seem that the market would even be smaller.
I would also guess that in a fan without this feature there would be a serious space issue, it would be hard if not illeagel for X-10 to make something that fit in the decrative cover plate offering no protection against setting your ceiling on fire if the device fails, in my fans they are in a module that is about 2 inches deep and the dia of the fan control section and whild the parts would clearly fit in the space under the decrative mount I am guessing they are not there for safety reasons.
It is a great idea, which is why so many fan makers offer it at least as a add-on module but I think it would be a very hard retrofit for X-10 to come up with a product that was safe and would fit in that space under the decrative cover, many of them are pretty thin.
My suggestion -- replace your fan, you can do it for under 100 bucks, chance of getting a "hum" from the control is about zero, you can do it without ceiling access, and the chances of burning your house down is reduced to about zero. Besides that you will probably end up with a much nicer fan and for a cost not much more that 2 inlines, a crawl through the ceiling and in an install that requires you to take down the existing fan to rewire it.
Just a thought.
http://www.homedepot.com/webapp/wcs/stores/servlet/ProductDisplay?storeId=10051&langId=-1&catalogId=10053&productId=100630845&N=10000003+502796+10202007+4294965594The 44 In. Midili Fan in a Brushed Nickel finish comes with 5 Reversible Blades in a Black and a Rosewood finish. It also comes with a Single Frosted Opal Glass Light Kit that uses 2 Candelabra E12 Base Bulbs, at 40 Watt Max.
5 Reversible Blades (Black / Rosewood)
Single Frosted Opal Glass Light Kit
Brushed Nickel Finish
Uses 2 Candelabra E12 Base Bulbs, 40 Watt Max. (Included)
MFG Brand Name : Hampton Bay
Fan Width : 44 In.
Indoor or Outdoor : Indoor
Remote Control : Yes
Reverse : Yes